In a right angled triangle with an angle θ<90°, the trigonometric ratios sin, cos and tan are defined by

where opposite and adjacent refer to the side lengths of the sides opposite and adjacent to θ, while hypotenuse is the length of the longest side.

To remember these ratios, you can use the abbreviation sohcahtoa:

Example

Find cosθ in the triangle below.

From sohcahtoa we know cosθ=ha​. We can see in the diagram that o=4 and h=5. To find a, we use Pythagoras' Theorem:

So cosθ=53​.